The NISAR observatory’s most prominent feature is the large 39-foot (12 m) stationary antenna reflector mounted on a 30-foot (9 m) boom. The reflector is made of a gold-plated wire mesh that focuses the radar signals emitted and received by the upward-facing feed on the instrument structure. During the transmit phase, a radar signal is sent up to the reflector, which focuses and bounces it down to Earth at an angle, illuminating a 150-mile (242 km) swath. Radar signals bouncing upward off the ground hit the reflector and are focused back onto the radar feed to be processed.

The challenges of such a large antenna include stowing (folding) it to fit within the small space in the launch vehicle fairing and deploying it in multiple steps, during which it expands and locks into place much like a folding camp chair. NISAR’s antenna is of the same material and similar design as NASA’s Soil Moisture Active Passive (SMAP) mission (but it does not spin like SMAP’s). The reflector is built by Astro Aerospace in Carpinteria, California, a Northrop Grumman company, and supplied as part of NASA’s contribution to the mission.

The radar instruments and boom supporting the reflector are mounted to an octagonal instrument structure provided by NASA.